Allow icomplete types in scoped_refptr<T>.

base/memory/ref_counted.h

Index: base/memory/ref_counted.h
diff --git a/base/memory/ref_counted.h b/base/memory/ref_counted.h
index 960c8a28453122a5e00a2cb72d5f420e7b642f15..c9ba42401ed43976aa3e0317d72906cc81e612ab 100644
--- a/base/memory/ref_counted.h
+++ b/base/memory/ref_counted.h
@@ -271,41 +271,46 @@ class scoped_refptr {
 
   scoped_refptr() {}
 
-  scoped_refptr(T* p) : ptr_(p) {
+  scoped_refptr(T* p) : ptr_(p), ptr_caller_(&PtrCallerImpl) {
     if (ptr_)
-      AddRef(ptr_);
+      ptr_caller_(ptr_, PtrCall::AddRef);
   }
 
   // Copy constructor.
-  scoped_refptr(const scoped_refptr<T>& r) : ptr_(r.ptr_) {
+  scoped_refptr(const scoped_refptr<T>& r)
+      : ptr_(r.ptr_), ptr_caller_(r.ptr_caller_) {
     if (ptr_)
-      AddRef(ptr_);
+      ptr_caller_(ptr_, PtrCall::AddRef);
   }
 
   // Copy conversion constructor.
   template <typename U,
             typename = typename std::enable_if<
                 std::is_convertible<U*, T*>::value>::type>
-  scoped_refptr(const scoped_refptr<U>& r) : ptr_(r.get()) {
+  scoped_refptr(const scoped_refptr<U>& r)
+      : ptr_(r.get()), ptr_caller_(&PtrCallerImpl) {
     if (ptr_)
-      AddRef(ptr_);
+      ptr_caller_(ptr_, PtrCall::AddRef);
   }
 
   // Move constructor. This is required in addition to the conversion
   // constructor below in order for clang to warn about pessimizing moves.
-  scoped_refptr(scoped_refptr&& r) : ptr_(r.get()) { r.ptr_ = nullptr; }
+  scoped_refptr(scoped_refptr&& r) : ptr_(r.get()), ptr_caller_(r.ptr_caller_) {
+    r.ptr_ = nullptr;
+  }
 
   // Move conversion constructor.
   template <typename U,
             typename = typename std::enable_if<
                 std::is_convertible<U*, T*>::value>::type>
-  scoped_refptr(scoped_refptr<U>&& r) : ptr_(r.get()) {
+  scoped_refptr(scoped_refptr<U>&& r)
+      : ptr_(r.get()), ptr_caller_(&PtrCallerImpl) {
     r.ptr_ = nullptr;
   }
 
   ~scoped_refptr() {
     if (ptr_)
-      Release(ptr_);
+      ptr_caller_(ptr_, PtrCall::Release);
   }
 
   T* get() const { return ptr_; }
@@ -321,23 +326,19 @@ class scoped_refptr {
   }
 
   scoped_refptr<T>& operator=(T* p) {
-    // AddRef first so that self assignment should work
-    if (p)
-      AddRef(p);
-    T* old_ptr = ptr_;
-    ptr_ = p;
-    if (old_ptr)
-      Release(old_ptr);
+    Assign(p, &PtrCallerImpl);
     return *this;
   }
 
   scoped_refptr<T>& operator=(const scoped_refptr<T>& r) {
-    return *this = r.ptr_;
+    Assign(r.ptr_, r.ptr_caller_);
+    return *this;
   }
 
   template <typename U>
   scoped_refptr<T>& operator=(const scoped_refptr<U>& r) {
-    return *this = r.get();
+    Assign(r.get(), &PtrCallerImpl);
+    return *this;
   }
 
   scoped_refptr<T>& operator=(scoped_refptr<T>&& r) {
@@ -354,11 +355,13 @@ class scoped_refptr {
   void swap(T** pp) {
     T* p = ptr_;
     ptr_ = *pp;
+    ptr_caller_ = &PtrCallerImpl;
     *pp = p;
   }
 
   void swap(scoped_refptr<T>& r) {
-    swap(&r.ptr_);
+    std::swap(ptr_, r.ptr_);
+    std::swap(ptr_caller_, r.ptr_caller_);
   }
 
   explicit operator bool() const { return ptr_ != nullptr; }
@@ -379,33 +382,41 @@ class scoped_refptr {
   }
 
  protected:
+  enum class PtrCall { AddRef, Release };
+  using PtrCallerFunction = void (*)(T* ptr, PtrCall call);
+
+  static void PtrCallerImpl(T* ptr, PtrCall call) {
+    switch (call) {
+      case PtrCall::AddRef:
+        ptr->AddRef();
+        break;
+      case PtrCall::Release:
+        ptr->Release();
+        break;
+    }
+  }
+
   T* ptr_ = nullptr;
+  PtrCallerFunction ptr_caller_ = nullptr;
 
  private:
-  // Friend required for move constructors that set r.ptr_ to null.
   template <typename U>
   friend class scoped_refptr;
 
-  // Non-inline helpers to allow:
-  //     class Opaque;
-  //     extern template class scoped_refptr<Opaque>;
-  // Otherwise the compiler will complain that Opaque is an incomplete type.
-  static void AddRef(T* ptr);
-  static void Release(T* ptr);
+  void Assign(T* p, PtrCallerFunction caller) {
+    // AddRef first so that self assignment should work
+    if (p)
+      caller(p, PtrCall::AddRef);
+    T* old_ptr = ptr_;
+    PtrCallerFunction old_caller = ptr_caller_;
+    ptr_ = p;
+    ptr_caller_ = caller;
+    if (old_ptr)
+      old_caller(old_ptr, PtrCall::Release);
+    // Release above can potentially delete this object
+  }
 };
 
-// static
-template <typename T>
-void scoped_refptr<T>::AddRef(T* ptr) {
-  ptr->AddRef();
-}
-
-// static
-template <typename T>
-void scoped_refptr<T>::Release(T* ptr) {
-  ptr->Release();
-}
-
 // Handy utility for creating a scoped_refptr<T> out of a T* explicitly without
 // having to retype all the template arguments
 template <typename T>